Thermally responsive circuit breaker for electric cigar lighter



pril 26. 1966 A. T. LYBROOK 3,248,502

THERMALLY RESPONSIVE CIRCUIT BREAKER FOR ELECTRIC CIGAR LIGHTER FiledOct. 18, 1963 FIG. 2

IN VENTOR. Arm/d I Lybrook United States Patent Q 3,248,502 THERMALLYRESPONSIVE CIRCUIT BREAKER FOR ELECTRIC CIGAR LIGHTER Arnold T. Lybrook,Lancaster, Ohio, assignor to Essex Wire Corporation, Fort Wayne, Ind., acorporation of Michigan Filed Oct. 18, 1963, Ser. No. 317,247 3 Claims.(Cl. 200-122) This invention relates to a cigar lighter and, moreparticularly to an electrical circuit breaker for a cigar lighter, suchcircuit breaker being responsive to temperature.

The temperature responsive circuit breaker of this invention isparticularly adapted for use with an electric cigar lighter of the typecommonly used in motor vehicles. It has been a common practice toprotect such cigar lighters from overheating by use of thermallyresponsive circuit breakers connected in series with the electricalheating elements of such devices. Whenever the heating elements of thecigar lighters became overheated, the circuit breakers opened thecircuits to the heating elements. Some of the prior circuit breakers ofthis character were of the destructible fuse type or of the manuallyresettable latch type. The replacement or resetting of such circuitbreakers was in most instances a diflicult' or inconvenient operationfor the ordinary vehicle user. Other types of thermally responsivecircuit breakers which automatically reclosed upon the cooling of thecigar lighter heating elements were not entirely satisfactory as theywould repeatedly reenergize the heating elements with possible resultantdamage to the cigar lighters. The prior circuit breakers for cigarlighters also had other disadvantages such as being large, complex orexpensive.

It is, therefore, an object of this invention to provide an improvedthermally responsive circuit breaker for cigar lighters and the likewhich will substantially reduce the current flow to an overheatedheating element, thereafter maintain the current flow at such reducedvalue until the cause of over-heating has been obviated, and thenautomatically reestablish the normal energizing circuit for theci-garlighter.

Another object of this invention is to provide acircuit breaker of theforegoing character which has a small, simple construction of few partsand which may be economically manufactured and calibrated.

A further object of this invention is to provide a thermally responsivecircuit breaker which includes improved means -for supporting a heatingresistor adjacent a bimetal thermally responsive contact member.

These and other objects are attained in accordance with this inventionby providing a circuit breaker having a heat conducting first terminaladapted to be mounted in heat and electrical conducting relation withthe energizing terminal of -a cigar lighter socket having contact meansfor energizing the heating element of a cigar lighter igniting plug. Abimetal element is secured in heat and electrical conducting relationwith the first terminal and is movable in response to heat receivedtherefrom to disengage a pair of normally closed contacts shunting aheater resistor. This heater resistor is can ried by support members inheat transmitting relation with respect to the bimetal element so as tokeep the bimetal element in a contact disengaged position in response tocurrent flow through the resistor after dis engagement of the contacts.The bimetal element together with a spring clamp support member aresecured by the first terminal to a disc closing one end of a tubularhousing. The other end of the housing is closed by another disc to whicha support member carrying one of the contacts is secured by asecondterminal adapted to be connected to a source of power. The spring clampsupport member is formed with a resilient arm having an aperturereceiving one terminal end of the resistor with a snug fit and biasingthe other terminal end of the resistor into electrical engagement withthe support member.

Other objects and features of the invention will be apparent from thefollowing description and the accompanying drawing, in which: 7

FIGURE 1 is a side elevation view of a thermallyresponsive circuitbreaker embodying the invention;

FIGURE 2 is a sectional view taken along the line 2'2 of FIGURE 1,showing the contact member in closed-circuit position;

FIGURE 3 is an axial sectional view of a cigar lighter assembly shownwith the circuit breaker attached thereto, the contact member of thecircuit breaker being shown in open-circuit position; and

FIGURES 4 and 5 are perspective views of parts of the circuit breaker.

Referring to the drawing, there is shown a thermallyresponsive circuitbreaker comprising two generally circular end plates or discs 11 and 12,preferably stamped from sheet insulating material, and a tubular sheetmetal housing 13. The opposite edges of the side walls of the housing 13are provided with projecting lugs 14 engaging grooves 15 in the endplates 11 and 12 and crimped over the end plates 11 and 12 for holdingthe two end plates tightly to the housing 13. The various parts of thecircuit breaker 10 are secured to the end plates 11 and 12 in two mainsubassemblies 16 and 17, more particularly shown in FIGURES 4 and 5,respectively. A current-limiting heater resistor 18 is carried by thesubassernblies 16 and 17 in a manner to be described later.

The subassembly 16 includes the end plate 11 to which a spring clamp 19and a thermally responsive bimetal element 20 are secured by a terminalbushing 21. The spring clamp 19 is formed from a strip of suitableresilient material, such as brass, and comprises an arm 22 extending atan angle of substantially 60 with another arm 23. Each arm is providedwith an aperture, the arm 22 having a heater-engaging aperture 24 andthe arm 23 having an aperture 25 through which the terminal bushing 21passes. The bimetal element 20 is formed from thermostatic bimetalmaterial of the type comprising welded-together layers of metals havingdissimilar temperature coefiicients. The bimetal element 20 is generallyL-shaped and includes a thermally responsive arm portion 26 and anenlarged base portion 27. An electrical contact 28 comprising a sectionof contact metal in strip form is welded to the arm portion 2 6 near anend portion 29 that is formed at a angle with the arm portion 26. Thebase portion 2 7 is pro- I vided with a central aperture 30 throughwhich passes the terminal bushing 21. Two lugs 31 projecting from thebase portion 27 have their ends bent to extend into the slots 32 of theend plate 11 to prevent the bimetal element 20 from rotating relative tothe end plate 11. The base portion 27 of element 20 is also providedwith two extensions 33 between which is received a complemental lug 34extending from the arm 23 of the spring clamp -.19 to prevent the latterfrom turning relative to the bimetal element 20. The terminal bushing 21which is formed of a metal having high heat con ductivity such as brassis preferably tubular and internally threaded as indicated at 35. Theterminal bushing 21 passes through a suitable central opening in the endplate 11, the aperture 30 in the bimetal element 20 and the aperture 25in the spring clamp 19. The spring clamp or supporting member 19 and thebimetal elem9 ment are secured to the end plate 11 by turning the innerend 36 of the terminal bushing 21 over upon the arm 23 of the springclamp with a retaining flange 37 of the terminal bushing 21 engaging theouter side of the end plate 11.

The subassembly 17 includes a supporting member 41 preferably made fromsheet metal, which is secured to the end plate 12 by a terminal stud 41.The supporting member 41) is generally U-shaped and has twosubstantially parallel legs 42 and 43 connected at one end. At its freeend, the leg 42 is formed with a U-shaped slot 44 through which passesthe terminal stud 41. Two tabs 4-5 extending from the side edges of theleg 42 have their ends bent to extend into the slots 4-6 of the endplate 12 to prevent the supporting member from turning relative to theend plate 12. The free end of the leg 43 has a transversely bentextension or contact portion 47 to which is welded an electrical contact48 comprising a section of contact metal in strip form. The contact 48is preferably positioned at a right angle with respect to itscooperating contact 28. The leg 43 is provided with an elongated opening49 generally centrally thereof and extending to the contact portion 47.The terminal stud 41 which is formed of electrically conductive metal,such as brass, has a head 50 engaging the leg 42 of the supportingmember 41) and a threaded shank 51 passing through the slot 44 in theleg 42 and through a suitable central opening in the end plate 12. Theprojecting end of the shank 51 receives a washer 52 and a nut 53 whichis tightened to secure the supporting member 4t) to the end plate 12.

The heater 18 preferably is in the form of a well-known type ofelectrical resistor comprising a rigid rod-like core 60 with conductiveterminals 61 and 62 secured to the ends thereof. The core 611 may beformed of braided glass fiber strands having a conductive materialassociated therewith to provide the desired resistance value. The core60 has a substantial degree of rigidity resulting from a dielectriccoating applied thereto. The terminals 61 and 62 are preferablyidentical and each comprises a cylindrical metal band or cup secured, asby crimping, in good electrical and tight mechanical connection with thecore 60.

The terminals 61 and 62, respectively, of the resistor heater 18 arelocated in the aperture 24 of the spring clamp 19 and the opening 49 ofthe supporting member 40. The spacing of the inner end 36 of theterminal bushing 21 from the head 50 of the terminal stud 41 in theassembled circuit breaker 1t) obviously is somewhat greater than thelength of. the resistor heater 1%. To hold the heater 18 in place, theaperture 24 is contoured to closely fit the terminal 61. That is, thediameter of the aperture 24 is but slightly larger than that of theterminal 61 so as to enable ready insertion of the terminal into theaperture yet to cause the terminal to fit snugly in the aperture. Byreason of this snug fit, the heater 18 is supported in the arm 22 of thespring clamp 19 with its principal axis generally perpendicular to theplane of the arm 22. The opening 49 of the supporting member 40 hasrounded ends similarly contoured to closely fit the terminal 62 but hasa length somewhat greater than its width to facilitate insertion of theterminal 62 into the opening 49. It will be apparent that should theheater terminals 61 and 62 be of other shapes, the aperture 24 and theopening 49 would conform thereto.

Subsequent to the completion of the housing 13 and the subassemblies 16and 17, the arm 22 of the spring clamp 19 is flexed manually to aposition generally parallel withthe arm 23; and the terminal 61 of theheater resistor 18 is then inserted into the aperture 24. With the arm22 held in this generally parallel position, the subassemblies 16 and 17are fitted to the ends of the housing 13 in proper relation. As theseparts are fitted together, the terminal 62 of the heater 18 is insertedinto the opening 49 of the leg 43, after which the arm 23 is released.The lugs 14 of the housing 13 are then crirnped over the end plates 11and 12 to complete the assembly of the circuit breaker 10. Inasmuch asthe flexed arm 23 attempts to resume its initial position, it urges theheater 18 to the position shown in FIGURES 2 and 3 with the heaterterminal 62 in tight engagement with the end edge of the opening 49 ofthe supporting member 41 adjacent the contact portion 47. At the sametime, the resiliency of the spring clamp 19 also tends to turn the arm22 with respect to the heater terminal 61. As such turning movement islimited by the sung fit of the terminal 61 in the aperture 24, the arm22 at the edges of the aperture 24 will thereafter bear firmly on theterminal 61 and hold the heater 18 thereon. Thus, the heater terminals61 and 62, respectively, have firm pressure contact and good electricalconnection with the spring clamp 19 and the supporting member 40.

The circuit breaker 10 preferably is calibrated prior to its assembly bythe accurate forming of the various parts. As the functioning ofthermostatic bimetal material follows definite physical laws, thecalibration of the circuit breaker 10 is effected by forming the endportion 29 of the bimetal element 20 in a predetermined relation withrespect to the mounting base portion 27 at a normal ambient temperature.Because the constructions of the circuit breaker parts provide for theirassembly in an accurately aligned relationship, the circuit breaker 11is operative at a desired temperature determined by the form andmaterial of the bimetal element 20.

Referring now to FIGURE 3, the circuit breaker 10 is shown attached to aplug-type automatic cigar lighter of conventional structure such as iscommonly used in motor vehicles. The cigar lighter includes a socket 71which may be mounted in the dashboard 72 of the motor vehicle and isthus in electrical connection with the grounded battery terminal of themotor vehicle. A terminal stud 73 of brass or other heat-conductivemetal is supported by the insulator 741 in the base of the socket '71.Bimetal latch contacts 75 are supported on the insulator 74 inelectrical connection with the terminal stud 73.

An igniting plug or unit 76 is removably received in the socket 71.Attached to the inner end of the igniting plug 76 is a heating'elementassembly comprising a shallow metal cup 77 containing a spiral woundheating coil or element 78 of fiat metal ribbon. The inner end of theheating element '78 is electrically connected to the main body of theigniting plug 76 so as to be in electrical connection with the socket71. The outer end of the heating element 78 is attached to the cup 77which is insulated from the main body of the igniting plug 76. The cup77 is adapted for cooperation with the bimetal latch contacts 75 toselectively establish an igniting or heating circuit under the controlof the user of the cigar lighter 70. The bimetal latch contacts 75function in a well-known manner to hold the igniting plug 76 in theheating position shown in FIGURE 3 until the heat from the heatingelement 78 causes outward movement of the bimetal latch contacts 75.Thereupon, the released igniter plug 76 moves to a normal position(not'shown) within the socket 71 from which the igniter plug 76 may bewithdrawn for use.

The terminal bushing 21 of the circuit breaker 10 is threaded upon theterminal stud '73 of the cigar lighter socket 71 to mount the circuitbreaker 10 upon the socket. It will be evident that the terminal bushing21 is in both heat-conductive and electrically-conductive relation withthe terminal stud 73. A connection may be made from the undergroundedterminal of the vehicle battery to the terminal stud 41 of the circuitbreaker 10.

In the normal, non-heated condition of the circuit breaker 10, as shownin FIGURE 2, the contacts 28 and 48 are engaged to provide a currentpath from the terminal stud 41 to the bimetal latch contacts 78 throughthe supporting member 40, contacts 28 and 48, bimetal element 20, springclamp 19, terminal bushing 21 and terminal stud 73. Upon the ignitingplug "76 being pushed into the socket 71 to establish a heating circuitthrough the cup 77 and the bimetal latch contacts 75, the resultantpassage of current flow through the heating element 78 raises itstemperature until the cup 77 is released by the bimetal latch contacts75. Some heat from the energized heating element 78 will be transferredto the base portion 27 of the bimetal element through the terminalbushing 21 and the terminal stud 73.

During normal operation of the cigar lighter 70, the bimetal element 20will not be heated sufficiently to cause separation of the contact 28from the contact 48. However, if for some reason, the heating element 78is energized for a longer period of time or is overheated because of ashort-circuit in the heating element 78, the excessive heating of theheating element 78 causes the bimetal element 20 to be heatedsufficiently to move the contact 28 out of engagement with the contact48. Upon separation of the contacts 28 and48, the heater 18 will beconnected in series circuit with the heating element 78. It will benoted that in the unheated condition of the circuit breaker the heater18 is effectively shortcircuited or shunted by the bimetal element 20through the contacts 28 and 48.

The heater 18 is selected to have a resistance value greater than thatof the heating element 78 so as to substantially reduce the current flowto the cigar lighter 70 when the contacts 28 and 48-separate. At thesame time, the resistance value of the heater 18 must be moderately lowto cause the current passing through it to generate enough heat to keepthe bimetal element 20 in open circuit position once the contacts 28 and48 have been separated and as long as current continues to flow throughthe circuit breaker 10. The particular resistance value of the heater 18depends upon the current rating of the heating element 78 but preferablyis on the order of twice the resistance value of the heating element 78.

In the event of a short circuit occurring in the cigar lighter socket71, it will be evident that the passage of the consequent high currentthrough the bimetal element 20 will result in the heating of the bimetalelement 20 by virtue of its resistance. Under such a condition, thecontacts 28 and 48 will be separated in the same manner as occurs whenthe heating element 78 becomes overheated to cause the current How tothe socket 71 to pass through the current-limiting resistor heater 18.The heat generated by the current flow through the heater 18 holds thebimetal element in open circuit position and prevents reclosure of thecontacts 28 and 48 while the excessive current condition exists.

It will be evident that when the abnormal condition which causesoperation of the circuit breaker 10 has been corrected, the circuitthrough the heater 18 is interrupted. The bimetal element 20 will thencool and return to its normal position with the contact 28 and 48engaged.

While the invention has been illustrated and described in its preferredembodiment and has included certain details, it should be understoodthat the invention is not to be limited to these precise details sincethe same may be carried out in other ways falling within the scope ofthe invention as claimed.

What is claimed is: 1

1. An improved circuit breaker for a cigar lighter having a socket inwhich a removable igniting plug having a heating element is adapted tobe received and manually moved into position to be heated and a heatconducting terminal having contact means thereon engaging said ignitingplug when said igniting plug is in position to energize said heatingelement, an improved circuit breaker comprising: a tubular housing; adisc of insulating material secured in each end of said housing; a firstheat conducting terminal member extending through and secured to a firstone of said discs and adapted to be mounted in heat and electricalconducting relation with the cigar lighter heat conducting terminal; asecond terminal member extending through and secured to the second ofsaid discs, and adapted for connection to a source of electrical power;a support member within said housing secured to said second disc inelectrical connection with said second terminal member by an innerportion thereof; a first electrical contact fixed on said first supportmember in electrical connection therewith; a thermally-responsivebimetal element within said housing secured to said first disc at oneend in heat and electrical conducting relation with said first terminalmember by an inner portion thereof, said bimetal element having a secondelectrical contact fixed on its other end in electrical connectiontherewith and normally engaging said first contact, said bimetal elementbeing movable in response to heat received from said first terminalmember upon a predetermined heating of said cigar lighter heatingelement to disengage said second contact from said first contact; aU-shaped spring clamp member within said housing having a first armsecured to said first disc.

in electrical connection with said bimetal element by said inner portionof said second terminal member, said spring clamp member having aresilient, free second arm provided with an aperture; and acurrent-limiting heater resistor within said housing comprising a rigid,rod-like core having first and second terminals secured to itsrespective ends, said first resistor terminal extending through saidaperture in said second arm of said spring clamp member and fittingsnugly in said aperture, said resistor having said second resistorterminal biased into electrical engagement with said support member bysaid spring clamp member whereby said resistor is shunted by saidbimetal element when said first and second contacts are in engagement,said resistor being supported in heat transmitting relation with respectto said bimetal element by said spring clamp member and said supportmember, the resistance value of said resistor being sufiicient to causethe current passing therethrough to generate enough heat to keep saidbimetal element in a disengaged contact position after disengagement ofsaid contacts.

2. An improved circuit breaker according to claim 1, wherein saidsupport member is provided with a slot for receiving said secondresistor terminal.

3. An improved circuit breaker according to claim 1, wherein saidbimetal element has a small resistance value relative to that of saidresistor but of a sufficient value to cause said bimetal member todisengage said second contact from said first contact in response toself-heating caused by an abnormally high current flow therethroughgreater than a predetermined value.

References Cited by the Examiner UNITED STATES PATENTS 1,701,757 2/1929Lea 200122 2,403,803 7/ 1946 Kearsley 200-122 2,704,318 3/1955 Jorgensenet al. 200116 X 2,914,637 11/1959 Wuerth 200122 BERNARD A. GILHEANY,Primary Examiner. L. A. WRIGHT, Assistant Examiner.

1. AN IMPROVED CIRCUIT BREAKER FOR A CIGAR LIGHTER HAVING A SOCKET INWHICH A REMOVABLE IGNITING PLUG HAVING A HEATING ELEMENT IS ADAPTED TOBE RECEIVED AND MANUALLY MOVED INTO POSITION TO BE HEATED AND A HEATCONDUCTING TERMINAL HAVING CONTACT MEANS THEREON ENGAGING SAID IGNITINGPLUG WHEN SAID IGNITING PLUG IS IN POSITION TO ENERGIZE SAID HEATINGELEMENT, AN IMPROVED CIRCUIT BREAKER COMPRISING: A TUBULAR HOUSING; ADISC OF INSULATING MATERIAL SECURED IN EACH END OF SAID HOUSING; A FIRSTHEAT CONDUCTING TERMINAL MEMBER EXTENDING THROUGH AND SECURED TO A FIRSTONE OF SAID DISCS AND ADAPTED TO BE MOUNTED IN HEAT AND ELELCTRICALCONDUCTING RELATION WITH THE CIGAR LIGHTER HEAT CONDUCTING TERMINAL; ASECOND TERMINAL MEMBER EXTENDING THROUGH AND SECURED TO THE SECOND OFSAID DISCS, AND ADAPTED FOR CONNECTION TO A SOURCE OR ELECTRICAL POWER;A SUPPORT MEMBER WITHIN SAID HOUSING SECURED TO SAID SECOND DISC INELECTRICAL CONNECTION WITH SAID SECOND TERMINAL MEMBER BY AN INNERPORTION THEREOF; A FIRST ELECTRICAL CONTACT FIXED ON SAID FIRST SUPPORTMEMBER IN ELECTRICAL CONNECTION THEREWITH; A THERMALLY-RESPONSIVEBIMETAL ELEMENT WITHIN SAID HOUSING SECURED TO SAID FIRST DISC AT ONEEND IN HEAT AND ELECTRICAL CONDUCTING RELATION WITH SAID FIRST TERMINALMEMBER BY AN INNER PORTION THEREOF, SAID BIMETAL ELEMENT HAVING A SECONDELECTRICAL CONTACT FIXED ON ITS OTHER END IN ELECTRICAL CONNECTIONTHEREWITH AND NORMALLY ENGAGING SAID FIRST CONTACT, SAID BIMETAL ELEMENTBEING MOVABLE IN RESPONSE TO HEAT RECEIVED FROM SAID FIRST TERMINALMEMBER UPON A PREDETERMINED HEATING OF SAID CIGAR LIGHTER HEATINGELEMENT TO DISENGAGE SAID SECOND CONTACT FROM SAID FIRST CONTACT; AU-SHAPED SPRING CLAMP MEMBER WITHIN SAID HOUSING HAVING A FIRST ARMSECURED TO SAID FIRST DISC